v=[1 0]';
c=[-3:1:3];
p=v*c;

subplot(131)
plot([-3 -3],[-3 3],'b','LineWidth',2)
hold on
plot([-2 -2],[-3 3],'b','LineWidth',2)
plot([-1 -1],[-3 3],'b','LineWidth',2)
plot([ 0  0],[-3 3],'b','LineWidth',2)
plot([ 1  1],[-3 3],'b','LineWidth',2)
plot([ 2  2],[-3 3],'b','LineWidth',2)
plot([ 3  3],[-3 3],'b','LineWidth',2)
grid on
axis square
axis([-3 3 -3 3])
text(0.2,0.2,'S_1')

subplot(132)
patch([0 0 3 3],[-3 3 3 -3],[0 0 1])
alpha(0.3)
grid on
axis square
axis([-3 3 -3 3])
text(0.2,0.2,'S_2')

subplot(133)
patch([-3 -3 3 3],[-3 3 3 -3],[0 0 1])
alpha(0.3)
grid on
axis square
axis([-3 3 -3 3])
text(0.2,0.2,'S_3')

